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Municipal Bond Guarantee (Details) $ in Millions | 1 Months Ended | 9 Months Ended | 12 Months Ended |
--- | --- | --- | --- | ---
Apr. 30, 2018 USD ($) | Sep. 30, 2018 USD ($) yr Contract | Sep. 30, 2017 USD ($) | Dec. 31, 2017 USD ($) Contract | Dec. 31, 2012 USD ($) | Jul. 31, 2012 USD ($)
Guarantor Obligations [Line Items] |  |  |  |  |  |
Repayments of debt |  | $ 11.2 | $ 364.6 |  |  |
Interest paid |  | 5.3 | $ 0.5 |  |  |
Total gross unearned insurance premiums |  | 156.2 |  | $ 136.8 |  |
HG Global |  |  |  |  |  |
Guarantor Obligations [Line Items] |  |  |  |  |  |
Partners capital contribution |  |  |  |  | $ 594.5 |
Surplus notes |  | $ 499.0 |  |  |  | $ 503.0
Assets held-in-trust |  |  |  | $ 603.0 |  |
HG Global | Preferred Stock |  |  |  |  |  |
Guarantor Obligations [Line Items] |  |  |  |  |  |
Ownership interest (as a percent) |  | 96.90% |  | 96.90% |  |
HG Global | Common Stock |  |  |  |  |  |
Guarantor Obligations [Line Items] |  |  |  |  |  |
Ownership interest (as a percent) |  | 88.40% |  | 88.40% |  |
BAM |  |  |  |  |  |
Guarantor Obligations [Line Items] |  |  |  |  |  |
Percentage of Risk Premium Ceded |  | 60.00% |  |  |  |
Year of U.S. Treasury rate | yr |  | 1 |  |  |  |
Contracts outstanding | Contract |  | 7,184 |  | 6,371 |  |
Remaining weighted average contract period outstanding (in years) |  | 10 years 10 months |  | 10 years 11 months |  |
Municipal bond outstanding principal |  | $ 47,259.1 |  | $ 42,090.6 |  |
Municipal bond outstanding interest |  | 23,707.4 |  | 21,057.1 |  |
Municipal bond debt service outstanding |  | 70,966.5 |  | 63,147.7 |  |
October 1, 2018 - December 31, 2018 |  | 3.3 |  |  |  |
2019 |  | 13.1 |  |  |  |
2020 |  | 12.6 |  |  |  |
2021 |  | 12.1 |  |  |  |
2022 |  | 11.5 |  |  |  |
2023 and thereafter |  | 103.6 |  |  |  |
Total gross unearned insurance premiums |  | 156.2 |  |  |  |
HG Global |  |  |  |  |  |
Guarantor Obligations [Line Items] |  |  |  |  |  |
Collateral held in supplement trust |  | 741.7 |  | 715.1 |  |
Interest receivable |  | $ 143.2 |  | 126.0 |  |
HG Re |  |  |  |  |  |
Guarantor Obligations [Line Items] |  |  |  |  |  |
Percentage of par value of policy reinsured |  | 15.00% |  |  |  |
BAM |  |  |  |  |  |
Guarantor Obligations [Line Items] |  |  |  |  |  |
Surplus notes |  | $ 499.0 |  | $ 499.0 |  |
BAM Management |  |  |  |  |  |
Guarantor Obligations [Line Items] |  |  |  |  |  |
Partners capital contribution |  |  |  |  | $ 14.5 |
Surplus Note | BAM |  |  |  |  |  |
Guarantor Obligations [Line Items] |  |  |  |  |  |
Derivative, fixed interest rate (as a percent) |  | 4.60% |  | 3.78% |  |
Surplus Note | BAM |  |  |  |  |  |
Guarantor Obligations [Line Items] |  |  |  |  |  |
Repayments of debt |  |  |  | $ 4.0 |  |
Interest paid |  |  |  | 1.0 |  |
Combination One | Surplus Note | BAM |  |  |  |  |  |
Guarantor Obligations [Line Items] |  |  |  |  |  |
Number of years of change in interest rate | yr |  | 5 |  |  |  |
Combination Two | Surplus Note | BAM |  |  |  |  |  |
Guarantor Obligations [Line Items] |  |  |  |  |  |
Number of years of change in interest rate | yr |  | 3 |  |  |  |
US Treasury Rate | Surplus Note | BAM |  |  |  |  |  |
Guarantor Obligations [Line Items] |  |  |  |  |  |
Basis spread on variable rate |  | 3.00% |  |  |  |
Fixed interest rate | Surplus Note | BAM |  |  |  |  |  |
Guarantor Obligations [Line Items] |  |  |  |  |  |
Derivative, fixed interest rate (as a percent) |  | 8.00% |  |  |  |
First Quarter, year two | BAM |  |  |  |  |  |
Guarantor Obligations [Line Items] |  |  |  |  |  |
2019 |  | $ 3.3 |  |  |  |
Second Quarter, year two | BAM |  |  |  |  |  |
Guarantor Obligations [Line Items] |  |  |  |  |  |
2019 |  | 3.3 |  |  |  |
Third Quarter, year two | BAM |  |  |  |  |  |
Guarantor Obligations [Line Items] |  |  |  |  |  |
2019 |  | 3.3 |  |  |  |
Fourth Quarter, year two | BAM |  |  |  |  |  |
Guarantor Obligations [Line Items] |  |  |  |  |  |
2019 |  | 3.2 |  |  |  |
Series A BAM Surplus Note | HG Global |  |  |  |  |  |
Guarantor Obligations [Line Items] |  |  |  |  |  |
Surplus notes |  |  |  | 203.0 |  |
Series B BAM Surplus Note | HG Global |  |  |  |  |  |
Guarantor Obligations [Line Items] |  |  |  |  |  |
Surplus notes |  |  |  | $ 300.0 |  |
BAM | Fidus Re Ltd. |  |  |  |  |  |
Guarantor Obligations [Line Items] |  |  |  |  |  |
Losses above retention, percentage of liability | 90.00% |  |  |  |  |
Fidus Re Ltd. | BAM |  |  |  |  |  |
Guarantor Obligations [Line Items] |  |  |  |  |  |
Collateralized financial guarantee, term | 12 years |  |  |  |  |
Aggregate losses on ceded business | $ 165.0 |  |  |  |  |
Losses above retention, percentage of liability | 10.00% |  |  |  |  |
Minimum | Fidus Re Ltd. | BAM |  |  |  |  |  |
Guarantor Obligations [Line Items] |  |  |  |  |  |
Aggregate losses on ceded business | $ 165.0 |  |  |  |  |
Maximum | Fidus Re Ltd. | BAM |  |  |  |  |  |
Guarantor Obligations [Line Items] |  |  |  |  |  |
Aggregate losses on ceded business |  | $ 276.0 |  |  |  |

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